The raw material powder for use in powder metallurgy technology (hereinafter referred to as a raw material powder for powder metallurgy) is produced by mixing an iron powder as a basic component, a metal powder containing an alloy component (hereinafter referred to as an alloying powder), and a binding agent for fixing the alloying powder (or at least some of them) to the surface of the iron powder (hereinafter referred to as a binding agent). Moreover, a raw material powder for powder metallurgy containing, as required, one or two or more members selected from lubricant powders, flow enhancing agents, free-machining agent powders, and lubricant powders for sliding surface is also used.
In the raw material powder for powder metallurgy, it is required that the alloying powder is fixed to the surface of the iron powder through the binding agent and the lubricant powder, the flow enhancing agent, the free-machining agent powder, the lubricant powder for sliding surface, and the like, which are added as required, are uniformly mixed. Then, various mixing methods have been examined.
For example, Japanese Unexamined Patent Application Publication No. 2-47201 (Patent Document 1) discloses a technology for adding an alloying powder, a free-machining agent powder, and a lubricant powder to an iron powder and performing first mixing, adding a binding agent and performing second mixing while increasing the temperature, and performing third mixing while cooling.